Balers are machines that pick-up crop that has been deposited in windrows or swathes and compact it into bales. The crop may be, for example, straw that has been deposited by a combine harvester or grass cut by a mowing machine. The balers themselves can be self-propelled or towed by a tractor and the bales can be round or square. The present invention is particularly concerned with square balers but is not restricted to any particular crop.
As with all balers, a square baler has a pick-up for raising the crop from the ground, a crop transport mechanism and a baling chamber. The transport mechanism in a square baler comprises feeder duct that acts as a pre-compression chamber into which the crop is introduced and in which the crop is pre-compressed by a packer. Sometimes a cutter is provided at the lower end of the intake feeder duct to chop the crop before it is formed into bales.
When a desired degree of compression has been reached in the intake feeder duct, as detected for example by movement of a spring biased flap in the wall of the intake feeder duct, a so-called stuffer is actuated to upload the contents of the intake feeder duct into a square baling chamber where it is compressed further to form a bale. The bale is built up in slices in this way until the desired bale length is reached.
The compression of the crop in the baling chamber is carried out by a constantly reciprocating plunger which pushes the bale being formed against a resistance offered by a previously formed bale that is in the process of being ejected from the baling chamber. To set its resistance to movement, the previously formed bale is gripped from the sides and/or from above by walls to which a hydraulic pressure is applied in a direction to compress the bale.
The hydraulic pressure that is varied to regulate the density of the bale being formed can be set manually or automatically. In the latter case, instead of manually setting the magnitude of the hydraulic pressure, the operator sets a desired degree of resistance. The actual degree of resistance is measured, for example from the reaction force on the plunger, and compared with the desired resistance to derive an error signal. The hydraulic pressure is then varied in a closed feedback control loop to minimise the error signal and thereby attain the desired resistance set point.
A sensor is provided that measures movement of a bale as it is being formed in order to determine its length. Once a bale in the baling chamber reaches the desires size, lengths of twine are wrapped around the bale and they are knotted to complete the baling process.
There are numerous operating parameters that can be set by the operator that affect baling quality, this term being used herein to refer both the quality of the bales themselves and to the baling efficiency, i.e. the weight of crop baled in a given time.
Bale quality is unacceptable if the bale density is too low or too high, if the bale length or weight is outside a specified range, if the bale density is not uniform across the width of the bale, or if the twine tension is too high or too low. Incorrect twine tension can result in bales of poor shape or bales that fall apart while they are being handled.
It has previously been proposed in EP 0276496 to construct a feeder duct of which the volume can varied by changing the distance between its two curved walls. In addition to such parameters as the tractor speed, the steering angle, and machine settings such as the twine tension and the degree of compression in the pre-baling chamber, the control of the volume of the feeder duct provides a further parameter that can be used to achieve the desired baling quality. However, because of the large number of parameters to be set and the fact that the settings are not all independent of one another, it is difficult for an operator, especially one who is inexperienced, to set the values of all the parameters correctly at the same time as driving at the correct speed and in the correct direction.